In a new interview with Variety, the Atomic Blonde star shares that she was looking for a role in a smaller film where she "could lose herself," which led her to reunite with her Young Adult director, Jason Reitman, for Tully. Theron plays a mother of three who gets a night nanny and the two form an unexpected bond. The part required her to gain weight, which she says was "harder for her now than when she was in her 20s."

"It was brutal in every sense," Theron, who previously put on 40 pounds for her Oscar-winning performance in the 2003 film, Monster, expresses. "This time around, I really felt it in my health. The sugar put me in a massive depression. I was sick. I couldn’t lose the weight. I called my doctor and I said, 'I think I’m dying!' And he’s like, 'No, you're 41. Calm down.'"

Theron will next star in Atomic Blonde, where she portrays a bad-ass international spy. During the filming, she had to go through intense training and ended up with bruised ribs, a twisted knee and even underwent extensive dental surgery after she cracked two teeth.

"It happened the first month of training," Theron tells Variety. "I had severe tooth pain, which I never had in my entire life. Having to cut one of the teeth out and root canals, it was tough. You want to be in your best fighting shape, and it’s hard. I had the removal and I had to put a donor bone in there to heal until I came back, and then I had another surgery to put a metal screw in there."

Watch the killer NSFW Atomic Blonde trailer in the video below. The action-packed film arrives in theaters on July 28.